1. Technical Field
The present invention concerns an ultra-wideband information transmission method. In addition the invention concerns an ultra-wideband transmitting apparatus, an ultra-wideband receiving apparatus and an ultra-wideband transmitting-receiving apparatus.
2. Discussion of Related Art
Ultra-wideband (UWB) data transmission methods operate with signals in pulse form, which are so shaped and arranged in the time domain that the result is a spectral power density distribution which is as homogenous as possible but which never exceeds the maximum permissible interference power within various frequency bands. UWB methods are attractive as they do not require a license and they allow high transmission capacities.
Instead of the modulated narrow-band carrier signals which are usual in wireless transmission, in the case of UWB data transmission methods short pulses of a pulse length in the range of nanoseconds or shorter are produced, which are of a broad frequency spectrum, for example from 3.1 GHz to 10.6 GHz. Data transmission methods are generally referred to as ultra-wideband (UWB) methods if the quotient of the sum and the difference of the two limit frequencies is 8 or less. In the stated example the quotient is about 2.1. In accordance with an alternative definition of ultra-wideband data transmission methods the bandwidth is to be at least 500 MHz.
Existing pulse-based ultra-wideband transmission methods suffer from the problem that they are only inadequately suitable for very high data rates. The reason for this lies primarily in the intersymbol interference (ISI) which increases upon an increase in the data rate.
An example of such a method is the method known by the trade mark “PulsON” from Time Domain, described in the document “PulsON® Technology Overview”, published on the Internet, for example at http://www.timedomain.com/Files/downloads/techpapers/PulsONOverview7—01.pdf.
With that method the information to be transmitted is encoded in the form of pulse position modulation. The spacing in respect of time of Gaussian single-cycle pulses used in that method, in relation to the respectively preceding pulse within a pulse sequence representing the bit is either 100 ps less (“0”) or 100 ps greater (“1”) than a bit-overlapping time spacing average value of 100 ns.
In that previously known method different channels are formed by an encoding in which single-cycle pulses are dispatched with a delay which obeys a pseudo-random sequence. A pseudo-random sequence is uniquely associated with each channel. Transmitter and associated receiver must have the same pseudo-random sequence in order to be able to communicate with each other on a channel. The receiver firstly decodes the channel encoding in the received signal by means of the pseudo-random sequence available to the receiver and then ascertains the information which is impressed on the signal by pulse position modulation.
For known systems like that one the upper limit of the possible data rate is determined by the following consideration: if there is a wish to increase the data rate the carriers of the information, the pulses (chips), must be emitted at spacings which are shorter in respect of time. If however those time spacings become very short, typically less than 50 ns, then signals of one and the same transmitter pulse, which overlap portion-wise in respect of time at the receiver antenna, can interfere, those signals arriving there over different paths for example by virtue of reflection phenomena or multi-path propagation. The association of individual pulses (chips) with a symbol (bit) at the receiver end is in that way made more difficult or becomes impossible. That means that the transmission is interfered with and the highest possible data rate exceeded.
The document Zeisberg, S; Müller, C.: Siemes, J.: Performance Limits of Ultra-Wideband Modulation Principles; IEEE Global Telecommunications Conference GLOBECOM01, 25 to 29 Nov. 2001, Vol. 2, pages 816-820 discloses distributing bit information to be transmitted in a UWB transmission method over many individual pulses (chips). As the value of a bit is distributed to a symbol over a relatively large number of individual pulses, reference is made in this connection to transmitter-end time spreading of the symbol. In the receiver the bit value is reconstructed by adding up the energy of the individual pulses (“soft integration of chip correlation”). Spreading of the information to many pulses however results in a dramatic reduction in the data throughput. To avoid that effect that document describes the possibility of introducing time overlap of different symbols (“time overlap between transmitted symbols”). An example of such a method is referred to as “overlapping pulse position modulation” (OPPM). The overlap of individual pulses of a symbol with those of other symbols however leads to unwanted collisions and thus bit errors.